The present invention is a process for the production of monosilanes from the high-boiling residue resulting from the reaction of hydrogen chloride with silicon metalloid in a process typically referred to as the "direct process." The process comprises contacting a high-boiling residue resulting from the reaction of hydrogen chloride and silicon metalloid, with hydrogen gas in the presence of a catalytic amount of aluminum trichloride effective in promoting conversion of the high-boiling residue to monosilanes. At least a portion of the aluminum trichloride catalyst required for conduct of the process may be formed in situ during conduct of the direct process and isolation of the high-boiling residue.
In the preparation of trichlorosilane by the direct process, a complex mixture is formed which is typically distilled to separate trichlorosilane from other components present in the mixture. After the trichlorosilane is distilled from the mixture, a high-boiling residue remains which boils above 80.degree. C. and above the trichlorosilane boiling point. The high-boiling residue can constitute as much as ten weight percent of the trichlorosilane in current commercial operations for the direct process. Therefore, it is desirable to convert the high-boiling residue into commercially valuable products to reduce by-product disposal and to improve raw material utilization.
The "direct process" is well described in the patent literature, for example, in Rochow, U.S. Pat. No. 2,380,995 and Barry et al., U.S. Pat. No. 2,488,487. The high-boiling fraction remaining after the monosilanes overhead distillation is a complex mixture comprising higher boiling silicon containing compounds which have, for example, SiSi, SiOSi, and SiCSi linkages in the molecules. The high-boiling fraction may also contain particulate silicon and metals or compounds thereof. Typical high-boiling residues obtained from the direct process distillation product are described, for example, in Mohler et al., U.S. Pat. No. 2,598,435 and Barry et al., U.S. Pat. No. 2,681,355.
Wagner, U.S. Pat. No. 2,606,811, teaches a hydrogenation process where a compound containing a halogen and the Si--Si bond is heated to a temperature of at least 300.degree. C. in the presence of hydrogen. The resultant products are monosilanes, however there is no teaching of aluminum trichloride as a catalyst.
Atwell et al., U.S. Pat. No. 3,639,105, describe a process where hydrosilanes are produced by contacting a disilane with hydrogen gas under pressure and heating the mixture in the presence of a transition metal catalyst such as palladium on charcoal. Atwell et al. state that the disilane may be part of a mixture from the direct process.
Neale, U.S. Pat. No. 4,079,071, describes a process for preparing hydrosilanes in high yields by reacting methylchloropolysilanes with hydrogen gas under pressure at a temperature of from 25.degree. C. to about 350.degree. C. in the presence of a copper catalyst. Neale states that the methylchloropolysilanes can be those typically created as direct process by-products. Useful copper catalysts described by Neale include copper metal, copper salts, and complexes of copper salts with organic ligands.
Ritzer et al., U.S. Pat. No. 4,393,229, describe a process for converting alkyl-rich disilanes in a residue obtained from the manufacture of alkylhalosilanes to halogen-rich polysilanes. The process comprises treating an alkyl-rich disilane-containing residue with an alkyltrihalosilane or silicon tetrahalide in the presence of a catalyst and a catalytic amount of a hydrosilane reaction promoter at an elevated temperature. Ritzer et al. teach aluminum trichloride as a useful catalyst in their process when used with a hydrosilane promoter. Ritzer et al. further teach that the resulting halogen-rich polysilanes can, in a separate step, be cleaved to form monosilanes.
Bokerman et al., U.S. Pat. No. 5,175,329, describe a process for the production of organosilanes from the high-boiling residue resulting from the direct process that results in a net consumption of organotrichlorosilane. In the process, the high-boiling residue is contacted with an organotrichlorosilane and hydrogen gas in the presence of both a hydrogenation catalyst and a redistribution catalyst.
Ferguson et al., U.S. Pat. No. 5,430,168, describe a process for the production of monosilanes from the high-boiling residue resulting from the, "direct process", reaction of methyl chloride and silicon metalloid. The process comprises forming a mixture comprising an organotrihalosilane and high-boiling residue in the presence of hydrogen gas and a catalytic amount of aluminum trichloride. The process results in consumption of the organotrihalosilane and conversion of the high-boiling residue to useful monosilanes.
The present invention provides a process where a high-boiling residue comprising disilanes resulting from producing trichlorosilane is converted into commercially useful monosilanes. The process comprises contacting a non-methyl containing high-boiling residue resulting from the reaction of hydrogen chloride and silicon metalloid with, hydrogen gas in the presence of a catalytic amount of aluminum trichloride. Furthermore, at least a portion of the catalyst in the present process can be formed in situ during conduct of the direct process and isolation of the high-boiling residue.